The role of viruses and interferon (IFN) in human immunoregulatory disorders and in normal immune reactivity is presently under investigation. These studies demonstrate that IFN is frequently present in patients with autoimmune disorders and in selected instances, antibodies to IFN can also be demonstrated in these patients with active disease. Moreover, these studies show that defective IFN gamma production in vitro is frequently associated with certain lymphoid malignancies and autoimmune disorders. Mechanisms of regulation of immune reactivity by human IFN have also been delineated. Studies have been initiated to investigate the role of viruses, especially cytomegalovirus, in human immunoregulatory disorders.